The present invention relates to ballast and to a process for the production of ballast, which has a high stability and long service life, for railway track laying and road construction and dike systems used for example in costal protection. This ballast consists of ballast stones and a polyurethane foam based on a reaction mixture of selected polyisocyanates and selected compounds which contain isocyanate-reactive groups.
The demand for ballast used in railway track laying and road construction has increased sharply in recent years. One reason for this is certainly the general increase in population mobility and freight traffic. Rail traffic, in particular, comprises an ever-increasing proportion of high-speed trains with a large axle load. The enormous displacement forces they cause are transmitted via the rails to the sleepers and from there to the ballast. The stone formation changes over time and individual ballast stones become distorted, shifted and rounded, so the position of the tracks is changed, which requires cost-intensive and time-consuming repair work that must be carried out at regular intervals.
Various methods of consolidating ballast with the incorporation of plastics have already been described in the past. See, for example, DD 86201, DE-A 2063727, DE-A 2305536, DE-A 3941142, DE-A 19711437, DE-A 19651755, DE-A 3821963, DE-A 19811838, and JP-A 08157552.
DE-A 2063727 describes a method of reducing lateral track buckling due to lateral displacement forces. In this case, the binder is sprayed onto the ballast bed in the form of a high-viscosity plastic and the ballast stones are adhesively bonded together at the points of contact. A possible alternative is 2-dimensional adhesive bonding of the ballast stones by injection of the binder in the form of a 2-component synthetic resin.
A method of raising railway sleepers and road surfaces is described in DE-A 2305536 which requires the introduction of a swelling agent, which then solidifies. The swelling agent is, for example, a multicomponent plastic such as polyurethane foam. The liquid plastic is applied through a hole in the sleeper using a filling probe.
JP-A 8157552 describes the preparation of polyurethane resins which cure in the presence of moisture and are used to stabilize piles of stones. The polyurethane resins are prepared using aromatic polyisocyanates, monofunctional polyethers and amino-initiated polyethers, and are applied by means of spraying processes.
A common feature of all the known methods is that they produce ballast which can only be stabilized unselectively with the aid of plastics. Furthermore, in some cases the methods described rely on a relatively complicated application technology.
The object of the present invention was to provide an improved process for the production of ballast which allows stabilization of the ballast and at the same time ensures a long service life.
Surprisingly, the object of the invention could be achieved by the process of the present invention as described below.